Of the balanced chemical equations below, which one most correctly represents a combustion reaction? *
CH4 + 2 02 - CO2 + 2 H20
O
Ca0 + H20 - Ca(OH)2
O 2 N2 + 3 H2 - 2 NH3
O 2 Mg + 02 - 2 Mgo

Two friends at different locations want to communicate with each other by sending low energy signals. which of the following methods can they use to communicate? a) produce x-rays using colliding electrons and send them to radios, which capture sound b) send messages using infrared radiation, which travel in the form of waves c) send radio waves through intervening media like radio and television d) produce sound waves using microwaves from heated objects

11. phosphorus-32 is radioactive and has a half life of 14 days. how much of a 124 mg sample of phosphorus-32 is present after 56 days? a) 7.75 mg b) 15.5 mg c) 31.0 mg d) 62.0 mg

What was bohr’s contribution to the planetary model